Vacuum brake boosters require a vacuum supply from the engine in order to assist the pedal force to be generated by the driver. Currently, a sufficient vacuum supply for brake force assistance becomes more rare at an increasing rate in new engine technology such as gasoline direct injection engines or Diesel engines. Additional auxiliary energy becomes necessary to assist the driver in braking. In determined systems, the driver's force is converted into hydraulic pressure by means of a vacuum brake booster and a tandem master brake cylinder (TMC), said hydraulic pressure being measured by pressure sensors at the outlet of the tandem master brake cylinder. One possibility of the additional brake force assistance is realized in brake systems with active hydraulic brake force assistance in that additional hydraulic pressure is produced by means of a pressure increasing unit.
Due to inertias and clearances in the system and due to the limited capacity of the pump, it is problematic in this pressure development to achieve a uniform pressure buildup with a desired characteristic curve.